The drive mode of an industrial vehicle, such as a fork lift truck, must be frequently shifted between a forward drive mode and reverse drive mode during loading/unloading work.
In an industrial vehicle equipped with a conventional manual shift transmission, a series of operations must be carried out to achieve the rapid forward/reverse shifting of the drive mode, as follows.
(1) The vehicle is braked to reduce the running speed to an extent where to-and-fro running is possible.
(2) The clutch is disengaged to shift the transmission from the second speed to the low speed, and then the forward/reverse shift control lever is operated.
(3) The throttle valve is opened while the clutch is kept in a slipping engagement to invert the running direction of the vehicle.
The series of foregoing operations is carried out by making effective use of the long experience of the driver. Therefore, sometimes, the transmission is damaged by coercive forward/reverse shifting operation at a running speed where shift-down and forward/reverse shift are impossible. In a vehicle equipped with a manual transmission, a series of such intricate operations requires a high-level operating skill, and burdens the driver with difficult work. On the other hand, various vehicles including industrial vehicles, such as fork lift trucks, equipped with an automatic transmission have been proposed in recent years. Vehicles equipped with an automatic transmission are required to allow rapid forward/reverse shifting operation in a manner that can be carried out by a skilled driver without the difficult operations necessary for the forward/reverse shifting of the drive mode of a vehicle equipped with a conventional manual transmission.